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500 BCE
Alchemy
Traditionally, alchemy has revolved around the reconstruction and deconstruction of matter, as it is mainly composed of the four basic elements, wind, earth, water, and fire. The chemical composition of each of these elements was analyzed and has eventually led to the development of the periodic table. -
442 BCE
Democritus
In ancient Greece, Democritus had created what is known to be the atomist doctrine. This illustrates how the entire universe consists of "countless corpuscles" , otherwise referred to as atoms, all with an identical composition. Atoms were known to be indivisible by nature, hence where it's name came from, as atom in Greek means inseparable. -
440 BCE
Empedocles
Historically, Empedocles was known for his theory regarding the central elements that make up all the substances on Earth. This consisted of four pure and indestructible elements; earth, air, water and fire. -
John Dalton
In 1803, John Dalton proposed several concepts that would eventually become the building blocks of future scientific discoveries. He theorized that all matter is composed of atoms, which are indivisible and cannot be destroyed. His theory also suggested that all atoms are identical, but vary in mass and quantity in every element. -
Marie Curie
A French chemist named Marie Curie conducted most of her research on radioactivity. In her lifetime she was awarded two Nobel Prizes due to her discovery of the radiation therapy that we use in medicinal practices today. She found that when radium was imposed upon tumor cells, they were destroyed at a faster rate than normal cells. Curie is also very well known for her discovery of the elements polonium and radium, where her and her husband were then awarded a Nobel Prize for their findings. -
Max Planck
Max Planck is commonly known for his quantum theory. He wanted to explain the concept behind bright colours from hot glowing matter. He hypothesized that energy was radiated in discrete and minute packets, as he later on referred to them as quanta. This correlates with Niels Bohr's theory, which illustrates a less detailed version of what happens when electrons move from one energy level to the other. Planck furthered explored the processes that occur when matter is emitting heat and light. -
J. J. Thomson
Thomson's contribution to the atomic theory was absolutely critical, as he discovered the electron. He proposed that in every atom there are areas of positive and negatively charged matter, leading to his development of the Plum Pudding model. His theory was phrased as "a sea of uniform positive charge" with negatively charged electrons circulation throughout each atom. -
Hantaro Nagaoka
During the Meiji period, Hantaro Nagaoka (a Japanese physicist) became a pioneer and major contributor to Japanese physics. In 1904, Nagaoka developed a model known as the Saturnian model and it was the first of it's kind to contain a nucleus. It was referred to as the Saturnian model as it displayed the different energy levels in the form of rings, similar to the rings of Saturn. In 1911 his discovery was recognized by Rutherford acting as a key component to Rutherford's future research. -
Albert Einstein
A significant part of the atomic theory is the atom itself and until 1905, scientists weren't able to prove that they existed. Thanks to a botanist named Robert Brown, Einstein used Brownian Motion and the connection between pollen grains and water to mathematically determine the size of the water molecules. This provided him with enough information to accurately concur the presence of atoms, as the water molecules were moving and interacting with each individual pollen grain or atom. -
Ernest Rutherford
Ernest Rutherford is commonly known for his postulation regarding the nuclear structure of an atom. The experiment that was conducted consisted of alpha particles being fired into gas atoms. This resulted with several particles being violently deflected. Ultimately, enabling Rutherford to infer that there is a dense, and positively charged region in each atom that makes up most of the atomic mass. -
Satyendra Nath Bose
An Indian theoretical physicist named Satyendra Nath Bose was known for his contributions to quantum mechanics. During the 1920s, Satyendra dedicated his time to exploring the relativity principle and quantum physics, as he was bale to derive this from Planck's constant. His research was then furthered and expanded upon by Einstein when they worked together, then forming the Bose-Einstein condensate many years later. -
Niels Bohr
In 1913, Niels Bohr's Planetary Model proposed that negatively charged electrons actually circle around the nucleus in different energy levels/ orbits. His theory also stated that when an electron moves from one energy level to the other, radiation is either emitted or absorbed. In other words, the energy is released and can be seen in the form of light. -
Louis De Broglie
In 1924, Louis De Broglie further explored the properties of electrons and whether they should be categorized as particles or as a wave property. When comparing both characteristics, De Broglie was intrigued as he found that electrons could be either one, incorporating a duality between the two. -
Wolfgang Pauli
Wolfgang Pauli was one of the many scientists that further developed Niels Bohr's model. In 1925, Pauli went on to present his theory, known as the Pauli Principle. This stated that two particles with half an integer spin cannot occupy the same quantum space simultaneously, resulting with both particles having opposing quantum spin values permanently. -
Werner Heisenberg
In 1925 Heisenberg introduced several concepts that contributed to the atomic theory, such as quantum mechanics as well as the uncertainty principle. Specifically, the uncertainty principle states that the momentum and position of a given particle (electron) cannot be determined exactly. Despite the proper equipment and procedures used, analyzing the location of an electron is near impossible as the subatomic connection would be disrupted, often times altering the position of the electron. -
Erwin Schrödinger
In 1926, Schrödinger expanded upon Niels Bohr's atom model and took it a step further. Through the use of mathematical equations, he was able to identify the likelihood of locating electrons in a given position. Compared to Schrödinger's quantum mechanical model, Bohr's model illustrated the direct path of an electron, whereas the quantum mechanical model was a more accurate means of predicting the odds of an electron being at a certain location. -
James Chadwick
In 1932, James Chadwick conducted an experiment that consisted of beryllium atoms being bombarded by alpha particles, resulting with the ejection of protons by an unknown radiation. From this, Chadwick interpreted this unknown radiation to be a type of subatomic particle that didn't have an affect on the overall charge of an atom, rather contributing to it's atomic mass. -
Lise Meitner
Lise Meitner, was an Austrian physicist who dedicated her work to exploring radioactivity. Lise led a group of physicists to nuclear fission through the use of uranium, when an extra neutron is absorbed. When bombarded by neutrons she found that the uranium atom would split. She discovered later on that there was a large amount of energy produced when nuclear fission occurs.This then guided scientists years later to create the first atomic bomb, referring to her as the mother of the atomic bomb. -
Chien-Shiung Wu
Chien-Shiung Wu was one of many women that were not directly recognized for their scientific contributions. One of the moments in her life that was quite distinct was in 1945, as she was offered a position at Columbia university where she would then investigate beta decay. This is when the nucleus of one element changes to another. Later on, her discoveries confirmed and greatly contributed to Enrico Fermi's beta decay theory. -
Robert LeRoy
Robert LeRoy is commonly known for his research regarding experimental kinetics, but later on changed to theoretical/ computational physics. His famous Leroy-Bernstein theory and the derivation of the LeRoy radius, are two areas of research that LeRoy was notorious for. As well as, he is the creator of an efficient software program that has helped scientists efficiently collect data during their experiments. -
Richard Bader
Richard Bader is notorious for his discovery on the importance of electron density, as it assists in explaining the behavior of atoms in a given molecule. His theory highlights that there are little to no atomic orbitals in each molecule, and unfortunately, his discovery wasn't accepted until he published his book, Atoms in Molecules. He later on went to expand the knowledge on quantum mechanics and translate it into an open system. -
Ronald Gillespie
Ronald Gillespie was a chemistry professor, who specialized in molecular geometry. His major contributions consisted of when he helped pioneer superacids and his exploration of bonding through valence shell repulsion and the factors that influence molecular structure. Ronald went on to study the shape of molecules and developed the commonly used valence shell electron pair repulsion theory. This enabled scientists to predict the shape of a molecule based on the electron pairs in the outer shell.
